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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #243313
Title: 3D Numerical Simulation of Turbulent Buoyant Flow and Heat Transport in a Curved Open Channel

Author
item CHAO, XIAOBO - University Of Mississippi
item JIA, YAFEI - University Of Mississippi
item WANG, SAM - University Of Mississippi

Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2009
Publication Date: 7/1/2009
Citation: Chao, X., Jia, Y., Wang, S.S.Y. 2009. 3D Numerical Simulation of Turbulent Buoyant Flow and Heat Transport in a Curved Open Channel. Journal of Hydraulic Engineering. 135(7), 554-563.

Interpretive Summary: In this study, a 3D numerical model was developed based on the CCHE3D hydrodynamic model to simulate the velocity and temperature distribution in a curved open channel. The effects of buoyancy on the momentum equations and turbulence transport equations were considered. For turbulence closure, the buoyancy-extended version of kappa-epsilon model was used. A comparison among the current numerical solution, the experimental measurement and Shen’s model prediction shows that the proposed model is capable of simulating flow fields and temperature distributions in curved open channels with reasonable accuracy. The results obtained from measurements and simulations show that there are two major and one minor secondary flow eddies at the 90 degree cross section for thermal flow of the experimental curved channel. However, in isothermal flow, there is only one secondary flow eddy. Both measurements and simulations show that in the flow with buoyancy effects, the secondary flow near the free surface moves towards inner bank, which is in opposite direction to that in isothermal flow. The maximum streamwise velocity is located near to the outer bank in the upper warmer water region, and it is about 20 to 30 percentages greater than the averaged velocity at inlet section. The vertical temperature distribution in the curved open channel was predicted well using this model. Due to the influence of secondary flow, the warmer layer is thicker near the outer bank than that near the inner bank at the 90 degree section. The advection along the interface of the upper and lower layers reduces the heat transport between two layers. At the 90 degree section isotherms show downward slopes from inner bank to outer bank, while near the outer bank, some of the isotherms slope upward. At this section, the maximum dimensionless temperature difference from inner bank to outer bank varies from 0.45 to 0.60. This study indicates that complex three-dimensional turbulent flows in curved channels with thermal buoyancy effects can be simulated numerically by the buoyancy-extended version of kappa-epsilon model with fine grid system. Some differences between the simulations and measurements were observed, and the needs for further improvements in numerical models, especially in turbulence closures and the influence of buoyancy force were realized.

Technical Abstract: A three-dimensional buoyancy-extended version of kappa-epsilon turbulence model was developed for simulating the turbulent flow and heat transport in a curved open channel. The density- induced buoyant force was included in the model, and the influence of temperature stratification on flow field was considered. The flow and temperature fields were simulated simultaneously. The model was validated by comparison with laboratory measurements, and the simulated fields were generally in good agreement with experimental data. A comparison of velocity fields in thermal and isothermal flow in curved open channel is presented and the effects of channel curvature and buoyant force on the velocity fields are also discussed.